1. Field of the Invention
The present invention relates to a semiconductor device as a main component of an onboard power inverter that controls an electric motor and the like. More particularly, the present invention is directed to a structure of a control substrate (circuit board) built in a semiconductor device of an onboard power apparatus that drives an AC power load from a DC power source, a connecting means or method between the control substrate and a power chip substrate, and a fixing means or method between the control substrate and an outer enclosing case.
2. Description of the Related Art
FIGS. 10 and 11 shows a structure of a semiconductor device called an intelligent power module (hereinafter also referred to as xe2x80x9cIPMxe2x80x9d) which is conventionally used as a driving device of an onboard power inverter. FIG. 10 is a top view of a power portion of the IPM in which a control substrate 7 is removed, and FIG. 11 is a side sectional view of the IPM.
In the respective drawings, a power chip substrate (circuit board)5 generally made of an insulating material is attached onto a metal plate 1 that is fixed to an outer enclosing case 2 of a resin mold, and a power chip 6 is mounted on the power chip substrate 5 by solder or the like. Leads 9a and 9b both the other ends of which are insert-molded are electrically connected through wire bonding to the power chip 6 and the outer enclosing case 2. Incidentally, reference numeral 3 in the drawing designates an upper cover, and 4a and 4b designate main electrodes.
On the other hand, through holes 20a and 20b for electrical connection to the power chip 6 are provided in the control substrate 7 on which relevant electrical parts 8 such as driving/protecting/controlling circuits for the power chip 6 are mounted. Connection between the control substrate 7 and the power chip substrate 5 has been conducted by soldering the leads 9a and 9b to the through holes 20a and 20b. 
In the foregoing related art, the leads 9a and 9b are soldered to the through holes 20a and 20b by means of manual soldering or a robot soldering apparatus. However, since the number of the leads 9a and 9b is large, it takes a long period of time for the assembling steps, which increases the assembling costs.
Further, when the semiconductor device was used in an onboard environment with a severe temperature cycle, solder cracks would often occur at their connection portions between the leads 9a and 9b and the through holes 20a and 20b. 
Besides, in the foregoing structure of the related art, the leads 9a and 9b are soldered to the through holes 20a and 20b in the control substrate 7. Accordingly, in the case where the control substrate 7, the power chip substrate 5 or the like results in trouble for some reason or other, it is impossible to remove only this control substrate 7. As a result, it is necessary to exchange the whole semiconductor device, which increases the repair cost and is not economical.
The present invention has been made in view of the foregoing problems, and therefore has an object of the invention to provide a high performance onboard semiconductor device having high reliability, low manufacturing costs, and low repair costs, in which improvement is made in regard to electrical connection between a power chip substrate and a control substrate, and in regard to a fixing method between the control substrate and an outer enclosing case.
According to a first aspect of the invention, an onboard semiconductor device comprises a power chip substrate on which a power chip is mounted, a control substrate provided with an electrical part in relation to the power chip, and an outer enclosing case in which the power chip substrate and the control substrate are contained, and is characterized in that the control substrate and the outer enclosing case are removably fixed to each other.
According to a second aspect of the invention, in the onboard semiconductor device of the first aspect of the invention, it is characterized in that means for fixing the control substrate to the outer enclosing case is a pawl projectingly provided on the outer enclosing case.
According to a third aspect of the invention, in the onboard semiconductor device of the first aspect of the invention, it is characterized in that means for electrically connecting the power chip substrate to the control substrate includes a lead electrically connected to the power chip and fixed to the outer enclosing case, and a connector attached to the control substrate so as to be fitted to the lead.
According to a fourth aspect of the invention, in the onboard semiconductor device of the first aspect of the invention, it is characterized in that means for electrically connecting the power chip substrate to the control substrate includes a conductive material member electrically connected to the power chip and fixed to the outer enclosing case, a conductive land provided on the control substrate for connection with the power chip, and an elastic electrical connection material intervening between the conductive material member and the conductive land, and the control substrate is fixed to the outer enclosing case in a state where the electrical connection material is compressed.
According to a fifth aspect of the invention, in the onboard semiconductor device of the first aspect of the invention, it is characterized in that means for electrically connecting the power chip substrate to the control substrate includes a lead which is electrically connected to the power chip, a lower end portion of which is fixed to the outer enclosing case, and which is worked into a spring shape, and the control substrate is fixed to the outer enclosing case in a state where a tip side of the lead is compressed.
According to a sixth aspect of the invention, in the onboard semiconductor device of the first aspect of the invention, it is characterized in that means for fixing the control substrate to the outer enclosing case is a securing member like a screw.